BR2 - Belgian Reactor 2
A (reactor) vessel full of medical solutions
One of the most powerful research reactors in the world
Belgian Reactor 2 (BR2) is a material testing reactor. Since it was started up in 1962, it has been one of the most powerful research reactors in the world. By testing nuclear fuels and materials, BR2 is contributing to guaranteeing the safety of current and future nuclear installations.
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The research reactor is also a vital player in the worldwide supply of medical radioisotopes, for the medical world in particular. Radioisotopes are used in nuclear medicine for the diagnosis and treatment of certain diseases, including cancer.
Other applications of BR2 can be found in the creation of radioisotopes for industry and in the production of high-quality semiconductors (doped silicon). These semiconductors are the basic material for the components of high-capacity electronics, as they are found in systems for solar and wind energy, hybrid cars, and high-speed trains, for example.
🎞️ Take a look inside BR2.
The cycles of BR2
The BR2 reactor operates on a schedule of successive cycles that include a period of shutdown and a period of operation (usually 21 days).The main purpose of the BR2 reactor is the irradiation of materials under high neutron flux (maximum thermal neutron flux of the order of 1015n.cm-2s-1). These materials are placed in installations, the complexity of which depends on the nature of the irradiation and the intended purpose. The reactor load (fuel elements, control rods) is established according to the objectives of the testers; it is adjusted each cycle.
Composition of BR2
BR2 is cooled by pressurised water (nominal value: 1.235MPa or 12.6kg/cm2 at the entrance of the reactor), which also serves as moderator. The beryllium matrix is composed of 79 cylindrical channels and contains fuel elements, control rods, experiment installations or reflector plugs made of beryllium. The fuel elements comprise six (sometimes fewer) concentric tubes, composed of a compound of uranium and aluminium and manufactured using the powder metallurgy technique. The sheets produced this way are covered on both sides with an aluminium alloy lining. The uranium used is highly enriched (90 to 93%) with the isotope 235U; weaker enrichments may be used in the future, preferably with increased uranium density in the fuel plates. The elements usually contain combustible neutron absorbers (B4C, Sm2O3) in the fuel plates.
The reactor is placed in a basin (the reactor dock) where the water height (more than 7m above the top lid) is such that it offers sufficient protection to the staff during the operation of the reactor. During reactor shutdown periods, the water level is lowered to allow access to the lid. Two auxiliary basins serve for underwater storage of irradiated materials and for gamma irradiation by means of fuel elements or control rods, unloaded from the reactor. The reactor's cooling is achieved by the forced circulation of water, which enters the vessel at the top and leaves the vessel at the bottom.
The reactor, the three basins and the reactor control room are located in a metal building, in the form of a domed cylinder whose density is regularly checked. In an adjoining building (machine building), there are several auxiliary facilities: a storage channel for underwater retention, which is connected to the reactor dock via a transfer tube; decommissioning cells connected to the storage channel; the pumps and heat exchangers for the reactor's primary cooling circuit; cleaning facilities for the different circuits; etc. Other buildings house the fans, air filters, electrical auxiliaries, air compressors, facilities for receiving and inspecting materials destined for the reactor, etc.
There are two types of control rods within BR2:
- one type for compensation and safety.
These can be ejected into the reactor to cause a rapid stop;
- and another type for regulation.
These regulatory rods are permanently connected to their displacement mechanism and thus cannot contribute to such a stop.
Their absorbent part consists of cadmium, coated with aluminium. Each rod moves in a conduction tube with cooling holes.
Monitors and detectors
The nuclear instrumentation consists of neutron monitors and radiation detectors, partly against the reactor, partly near the primary circuit at the reactor's exit. These send alarms and can command an automatic power reduction in the reactor. The speed of this reduction depends on the severity of the anomaly identified. Similar actions can be commanded by a whole host of monitors covering the cooling flow rate, cooling water pressure and temperature, contamination or radiation in water circuits or rooms, failures in the electricity or compressed air supply or for experiments.
The Beryllium matrix
The Beryllium matrix, which has been refreshed three times already (in 1980, 1996 and 2016), includes a large number of rods, in the form of hexagonal prisms with cylindrical bores (these form the reactor channels), assembled in such a way as to approximate a cylindrical structure. It is placed in the central part of the reactor vessel. This vessel, in aluminium alloy, includes an upper part and a lower part, in the form of truncated cones, connected on both sides to the central cylinder.
Lids made from stainless steel seal the vessel at both ends. The upper lid shows 79 circular openings, corresponding to the 79 channels for the central section in beryllium. Each opening is connected to one of these channels by means of a conduction tube; the openings are sealed with plugs during reactor operation. There are 18 round openings in the lower lid, which are normally sealed with plugs and are also connected to reactor channels. They allow passage from experimental installations to a shielded chamber, located below the reactor.
Fuel elements, control and safety rods, regulatory rods, experiments to be irradiated, or plugs made of beryllium can be inserted into the channels of the beryllium matrix; the configuration, as obtained by means of these elements, depends upon the experimental requirements and the criteria that must be met to ensure an operational fail-safe during the irradiation cycle.
Waste and effluents
Solid and liquid waste is collected and sent to Belgoprocess' waste treatment facilities. The gaseous effluents, after filtration, are discharged through a 60m-high chimney. It is possible to purify the atmosphere of the reactor building and its cells by means of activated carbon filters. A comprehensive system measures the activity of the water for the primary and secondary circuits, of the water of the docks and of the storage channel in the machine building, of the atmosphere of the reactor building, of the air discharged through the chimney, etc.